Brush holder device for truing commutators



Dec. 8, 1931. H. D. MUNDAY 1,335,513

BRUSH HOLDER D EVlCE FOR TRUING COMMUTATORS I I FiledMay 18, 1928 10 Sheets-Sheet 1 IN V EN TOR.

Dec. 8, 1931. H. D. MUNDAY BRUSH HOLDER DEVICE FOR TRUING COMMUTATORS Filed May 18, 1928 10 Sheets-Sheet 2 INVENTOR. HwuwflMu/uiay BY ATTORNEY.

Dec. 8, 1931. H. D. MUNDAY BRUSH HOLDER DEVICE FOR TRUING COMMUTATORS Filed May 18, 1928 4.0 Sheets-Sheet 3 IN VEN TOR.

ffarace B Mal/my smama 2%.

A TTORNEY Dec. 8, 1931 H. D. MUNDAY BRUSH HOLDER DEVICE FOR TRUING COMMUTATORS Filed May 18, 1928 10 Sheets-Sheet 4 ATTORNEY Horace flMzmday v Dec. 8, 1931. H. D. MUNDAY BRUSH HOLDER DEVICE FOR TRUING COMMUTATORS Filed May 18, 1928 10 Sheets-Sheet 6 INVENTOR. fi oraaeflflfwzdag LQA TTORNEY H. D. MUNDAY Dec. 8, 1931.

BRUSH HOLDER DEVICE FOR TRUING COMMU'IATORS Filed May 18, 1928 10 Sheets-Sheet '7 Swoeutoz form fi. m GHQ 0mm De. 8, 1931 H. D. MUNDAY 1,335,513

BRUSH HOLDER DEVICE FOR TRUING COMMUTATORS- File i May 18, 1928 l0 Sheets-Sheet 8 lllIllW/l/Il/A INVENTOR BY SMAAMLH k. ATTORNEY.

Dec. 8, 1931. MUNDAY4 1,835,513

BRUSH HOLDER DEVICE FOR TRUING COMMUTATORS l NVENTOR Horace fl Mummy .SfiMH ATTORNEY,

Dec. 8, 1931. H. D. MUNDAY BRUSH HOLDER DEVICE FOR TRUING COMMUTATORS Filed May 18, 1928 10 Sheets-Sheet 1.0

Y INVENTOR. Horace fiMzmday m A TT ORNEY Patented Dec. 8, 1931 HORACE D. MUNDAY, OF SCHENECTADY, NEVJ YORK BRUSH HOLDER DEVICE FOR- TRUING COMIVIUTATORS Application filed May 18,

This invention relates to current collectors and particularly to brush holders adapted for use with commutators or slip rings.

One object of my invention is to provide 5 a brush holder adapted for use with an abrasive member or with an abrasive brush wherein the parts are so arranged as to cause the member or'brush to exert a truing effect on the commutator of the machine with which 0 it is used.

A further object of the invention is to provide an improved brush holder adapted for use with an abrasive member or an abrasive brush and which will cause the member or brush to exert a truing effect on the commutator of the machine with which it is used. A further object of my invention is to provide a brush holder with means for advancing or feeding the brush toward the commutator and preventing or resisting any backward motion of the brush. A further object of the invention is to provide a brush holder adapted for use on a machine which is subj ect to heavy vibration and wherein the wear on the moving parts of the brush holder is reduced to a minimum. A further object of my invention is to lessen the rebound of brushes on high speed electric machines, which rebound is apt to occur when slight irregularities exist in the commutator surface.

Sooner or later, from one cause or another, flat spots develop in many commutators and slip rings. An abrasive cloth and abrasive stones applied by hand are the expedients that are generally tried first to keep the machines in proper working condition. This treatment is generally unsatisfactory and the commutator continues to get worse until finally the machine has to be shut down and the commutator trued by other methods. Small armatures are generally taken out of their frames and the commutators trued in w a lathe. The commutators of large machines 10 are some times trued in place by a portable grinding or turning device. This operation is apt to consume several days during which the machine is out of commission. Undercutting of the mica in the commutator is one remedy tried for these obvious disadvan- 1928. Serial No. 273,750.

tages. On small commutators undercutting of the mica is not satisfactory because the slots formed in the commutator by the undercutting are apt to fill up with dirt and burn out the armature.

In employing the devices constructed in accordance with the present invention, I overcome the disadvantages just noted. The operation of such devices is automatic and does not require the constant attention of the operator. Furthermore it does not or need not interfere with the normal operation of the machine.

The abrasive or active member employed for truing the commutator may be a block 35 formed of pure abrasive and adapted to be employed in a brush holder of the machine or otherwise associated with a brush holder, or the active member may contain conducting material in addition to abrasive material, and such member may function not only as the active truing element but also as one of the brushes of the machine.

In the preferred embodiments of my invention, means is provided for advancing the abrasive or active member toward the commutator and also for hindering the motion of the abrasive, that is, retarding or preventing motion of the abrasive toward or away from the commutator.

One effect of a hindering means employed by me is to prevent the abrasive from advancing quickly into a low spot of the commutator as the low spot passes under the abrasive and to confine the rubbing of the abrasive to the high spots of the commu tator. Or in case the abrasive does enter the low spot of the commutator the hindering means will offer a high resistance to the backward or retrograde motion of the abrasive as the abrasive is being pushed back by the commutator surface onto the high spot. In either of these cases the abrasive will be pressed less against or toward the low spots of commutator than against other portions of the commutator surface, with the result that ultimately the commutator will be ground to a true cylindrical or round surface.

The hindering means which I employ may ratus. Also, optionally, a sluggishl 1 yieldmg metal such as lead or solder, may be employed. In certain cases, to provide a hindering of the backward or retrograde movement of the abrasive I may'make use of thehigh resistance offered by a comparatively rigid grinding apparatus when the apparatus is caused to yield structurally a slight amount by the forcing backward of the abrasive by the high spot of the commutator. The weight ofthe grinding apparatus may contribute materially to this effect and, if desired, the apparatus may be weighted to increase its inertia.

The means of hindering the motion of the abrasive forms an important feature of the invention,together with the fact that the force for moving the abrasive is such that the advancement of the abrasive, radially at least, is harmlessly haltable on contact with the commutator.

With a viscous substance interposed to hinder the advancementof the abrasive towards the commutator, permitting the abrasive to move forward only slowly towards the com1nutator,the abrasive will slowly ad-v vance till it strikes the high parts of the re volving commutator. Since the speed of the commutator is so great in comparison with the slow speed of the abrasive that the abrasive'is not able to feed forward into the low spots of the commutator while the coinmutator is making one revolution, it is evident that the low spots of the commutator will not be touched till all the high spots have been worn down. Consequently the commutator must necessarily become true.

In the use of friction hindering means for truing up a commutator there is the difference that in the case of friction both the high part and the low part of the commutator are worn down at the same tin1e-the highpart being worn down heavily and the low part lightly. 'In the case of the viscous substance hindering means, as has been seen, the low part of the commutator is not touched at all till the high part has been worn down completely. How friction can be used to true up a commutator can be seen from the fact that the net force causing the advancement of the abrasive is only the excess :of the backward from the commutator than when the abrasive is merely stopped in its advancement towards the commutator. After the high level part of the commutator comes under the abrasive and the abrasive neces sarily ceases any further retrograde movement, the slight spring in the apparatus and its supports as a whole may be made to cause the abrasive to continue to exert the maximum pressure on the level high part of the commutator. Consequently since the abrasive exerts a heavy pressure on the high part of the commutator and a light pressure on the low part of the commutator, thecommutator will finally become true. i

Some of the metals or alloys have the property of yielding or bending slowly when subjected to a certain pressure. Lead is such a metal: solder is another. This property can be used in a'number ofways to give a slow motion, I For instance, a belt of lead or solder on pulleys will permit only a slow motion of the pulleys when the proper driving force is'applied.

WVhile in a preferred form of the invention the means used for hindering the motion of the abrasive are friction hinderingmeans and viscous substance hindering means, sluggishly yielding metal and in certain cases relief springs, structural yield, inertia clock mech- .anism and an oil or other fluid pump may 7 movement of time-measuring mechanism;

These means include the balance-wheel as disclosed in Figure '1 of my patent Number 1,727,112,.a piston and cylinder, slow motion of the piston being caused by water or oil being allowed to slowly leave the cylinder orv V to slowly enter the cylinder. 7

Other objects and advantages ofmy invention will appear from the following description taken in connection with the accompanying drawings wherein: Figure 1 is a side view, partly in section, of a brush holder embodying the preferred form of my invention;

Figure 2 is a detail sectional view taken 7 on .the line 2-2 of Figure 1; c

'Figure- 3 is a detail viewshowing a modification of the snubbing device shown in Figure 1.

Figure 4 is a view similar to Figure 1 but showing a modified form of the invention. Figure 5 is a detailsectional view taken on the line 5-'5 of Figure 4. .j V

Figure 6 is a detail sectional view taken on the'line 6 6 of Figure 5; i 1 Figure7 is a view similar to Figure l but showing a further modification; i

Figure 8 is a rear endelevation of the brush holder shown in Figure 7 I Figure 9 is afragmentary sectional view ofthe structure shown in Figure 8, the direction of view 'beingthe same as that of Figure 8;

Figure 10 is a perspective view of the pres sure finger shown in Figure 7 and parts integral therewith, including the pressure finger disc hub and auxiliary spring;

Figure 11 is a perspective view of part of the construction shown in Figures 7 and 8, this part being employed to cause friction on the pressure fin er;

Figure 12 is a site view of another modification;

' Figure 13 is a detail plan View of a port-ion of the structure shown in Figure 12;

- Figure 14 is a side view of another modification wherein a cord or wire is employed for retarding the motion of the pressure finger;

Figure 15 is a view similar to Figure 14 but showing a modification;

Figure 16 is a sectional view taken on the line 1616 of Figure 15;

Figure 17 is a view similar to Figure 15 but showing a further modification;

Figure 18 is a detail View showing a modification of the structure shown in Figure 17;

Figure 19 is a side view showing a still further modification;

Figure 20 is a sectional View taken on the line 20-20 of Figure 19;

Figure 21 is a side elevation, partly in section, showing a further modification Figure 22 is a perspective view of a part of the structure shown in Figure 21;

Figure 23 is a detail perspective view showing a modification of the structure shown in Figure 22;

Figure 24 is a view similar to Figure 23 but showing a still further'modification;

Figure 25 is a side or edge elevation, partly in section, showing a further modification;

Figure 26 shows a further modification;

Figure 27v is aside elevation of another modification showing means for positively advancing the brush toward the commutator;

Figure 28 is a sectional view on the line 2828 of Figure 27;

Figure 29 is a plan view of the structure shown in Figure 27;

Figure 30 is a perspective view of part of the structure shown in Figure 27;

Figure 31 is a side view, partly in section, of another modification in which the slow escape of fluid is used to give delayed action to the brush or active member; 7

V Figure 32 is a fragmentary plan view partly in section on the line 3232 of Figure 31;

Figure 33 is a detail view of an alternative construction Figure 3 1 is a side elevation of a further modification wherein means is provided for moving an abrasive block axially of the commutator;

Figure 35 is an end view, partly in section, of the structure shown in Figure 34;

Figure 36 is a perspective view of a part of the structure shown in Figures 34 and 35, and

Figure 37 is a side or end elevation showing a further modification.

In the form of my invention shown in Figures 1 and 2, a brush holder frame 1 is secured by a clamp 2 to the stationary stud 3 of an electric machine. The brush holder frame 1 is formed with a brush holder box 4 through which the brush 7 is adapted to be fed to contact with the commutator 8. Reference character 9a represents a brush pressure finger which is adapted to be actuated by a spring 10 to advance the brush through the brush holder box l; the pressure finger 9a transmitting its movement to the brush through the auxiliary spring 11 and brush engaging tip 12.

Through an elongated hole or opening 13 rimmed by the sides let of an enlarged portion of the pressure finger 9a, passes a tube 15 which is externally threaded for engagement with a nut 16. Nut 16 is sufiiciently reduced at opposite sides of its lower part 17 to enter the elongated opening 13 in the pressure finger; shoulder 18 of the nut bearing on the sides 14 of the pressure finger. The bore of the tube 15 is slightly enlarged at its lower end 19 to permit a collar 20 to be secured therein by peening over the lower edges 21 of the tube. A short rod 22 formed with a flange 23 intermediate its ends extends into the tube 15 and is pivoted at its lower end in brackets 2st secured to the brush holder frame 1 by screw 25; screw 25 serving an additional function of securing the terminal 26 of the brush pigtail 27. The upper end of rod 22 is slotted at 28 to receive and secure the lower end 29 of spiral spring 30, said lower end being suitably bent to enter the slot 28. Pin 31 serves to secure the lower end of the spring 30 to the rod 22.

The upper end 32 of the spiral spring 30 is made. secure to the tension adjusting cap 33, preferably by bending the end of the spring at right angles to enter the hole 34 in the cap 38 and bending over the upper end of the spring at 35 to hold the cap in place. The axial tension of the spring 30 holds the cap snugly against the tube 15.

By turning the tension-adjusting cap 33 in a clock-wise direction as viewed from the top, the tension of the spring 30 is increased there being provided a pin 36, adapted to enter slant-ing slots 37 in the rim of tube 15, to secure the tension adjusting cap in any desired position.

It is evident that the threaded tube 15 will tend to revolve under the action of spring 30 in a counter clock-wise direct-ion, always keeping the nut 16 pressed closely against the pressure finger 9a the nut 16 being kept from turning by the reduced or squared portion which engages the sides of the elongated opening 18. Consequently, all forward motion of the pressure finger 9a is held by ena. uv

nut 16. I

At thev outer end of the pressure finger 9a is a brush snubber bar 38 hinged to the member 39'secured to the pressure finger by" a screw 47. A snubber tension screw 41 passes freely throuoh' an opening 48 in the movable 7' snubber bar 38 and is threaded into the auxiliary spring .11.

pressure finger9r at 44. Asnubber relief spring 40 surrounds the screw 41; bearing at its lower and upper ends respectively against the snubber bar 38 and the tension adjusting nut 45. Anauxiliary spring limit screw 42 is threaded into the outer end of i the snubber bar 38 and is securely held in said bar by jam-nut 53.

Screw 42 passes freely through the hole 46 in the pressure finger 9a and is adapted to be adjusted as desired so to limit the bending or flexing of the By completely compressing the spring 40, by adujst-ment of the nuts 45, and by advancing the screw 42 to the tially perpendicular to the pressure finger.

The brush holder thus far described, in addition to the function of holding the usual brush and maintaining the brush in proper contact with the commutator, is adapted to I perform number of other useful functions.

Suppose that the commutator has a fiat spot in it which it 15 desired to grind out. An abrasive brush or an abrasive block is placed in the brush-holder box'4. The auxihary spring limit screw 42 is advanced into contact with the brush-engaging tip 12 of the auxiliary spring 11. Pressure is then puton the pressure finger 1n the usual way, that 1s, by

placing the arm 49 of the actuating spring in one of the notches 51 of the pressurefinger rise 52 and the arm 50 in a stationary notch. Tension is then put on the spiral spring 30 by turning the tension adjusting cap 33 clock wise, thus causing the threaded tube to re tateand advance the nut 16 to hold all advancement made by the pressure finger 9a.

Instead of using the springrlO to advance the pressure finger it may be left out of act1on altogether, dependence being had upon the nut 16 to advance the pressure finger as well as to hold all advancement made.

' r Under the combined action of the spring 10 and the spring 30, or spring alone if spring 10 18 left out of action it is evident that the brush or abrasive block will advance till it comes into Contact -'ith the commutator at the fiat spot. How hard the contact with the commutator at the flat spot will be depends on the stess of the springs 10 and 30, or

' the spring'80 alone spring 10 is not used ac r 4:- insane? gagement of the pressure finger with the With comparatively light" tension of the springs, the contact of the brush with the commutator at the fiat spot will be light, and therefore the wear-of the flat spot of-the commutator will be slight. When the liighzpart of the commutator comes under the brush and the brush is forced backwards the snubber reliefspri1w40 will be compressed. As'this snubber relief spring is short and relatively stiff, the high spot of the commutator will have to exert considerable pressure 'on'the brush before it is forced backwards. .Consequently there will be considerably more wear of the high spot of the commutator than of r the fiat spot with the result that the commutator will finally become'true;

Where the commutator is not badly out of round dependence can be made'on the lack of structural rigidity of the brushholder and supporting parts whichmay permit suificient yielding as the high spot of the commutator comes under'the brush to prevent the brush from being broken. Underthe reaction pressure of the brush as the high spot of the commutator comes under it, the yielding of the auxiliary spring 11 being annulled, the pressure finger will yield a little, thebr-ush-holder frame will yield a little, the brush-holder stud will yield a'little and the brush-holder yoke will yield a little, all-taken together amounting to some, thousandths of an inch. These various elements which are not designed for flexibility and are considered inflexible strength elements, will yield slightly under the reaction thrust of a high'part of the commutator, soas to permit the passing of the high part under the brush'and at the same time cause the brush to exert a relatively heavy pressure on the high part. As means is also provided for. advancing the brush as needed, this arrangement becomes an automatic truing device which does not require attention of an attendant.

The auxiliary spring limit screw 42, whether disposed as in Figure 1 or-thrleaded into theend of the pressure finger 9a may, in certain cases be omitted, provided the auxiliary spring 11 is brought forcibly up against the under side oft'he'pressure finger 9aby strongly tensioning. the spring 10 and spring 30 or by tensioning the spring 30 alone if spring 10 is not used. applied to the pressure finger, tending to advance or swing it downwardly, is suflicient to ca se a complete compression of the auxiliary spring 11. With this adjustment the brush 7 will bepressed more heavily into contact with the commutator than when spring 11 is allowed to function and as a result there will be somewhat more wear on the low spots of the commutator during the tr'uing opera- In this manner the force roe tion. However in certain caseswhere it is desirable that the brush advance quiclrly'into low spots-of the commutator rather than sluggishly, this adjustment, wherein the aux- 7 iliary spring is completely compressed, is of decided advantage.

In the operation of the device with the adjustment made as shown in Figure 1, that is, with the auxiliary spring 10 partially compressed and free to move in either direction, there is little if any truing effect on the commutator. This is because the difference in pressure exerted by the auxiliary spring in a position corresponding to that wherein the rush is in contact with a low spot of the commutator and the pressure exerted in another position a few thousandths of an inch away corresponding to that in which the brush is in contact with a high spot of the commutator, is not great enough to cause any substantial difference of wear between the low spot and high spot.

The brush holder thus far described is particularly designed to operate without excessive wear on the bore of the pressure finger hub 54 and the pin 55, particularly when the brush holder is employed merely as such and not as a truing device. lVhen used as a simple brush holder the pressure finger 9a is actuated as above described and auxiliary spring limit screw 42 is backed off to permit free play of the auxiliary spring 11. Under these conditions instead of continual vibration or swiveling movement of the pressure finger 9a, whatever vibration occurs will be taken up to a large extent by the spring 11 thus saving the pin 55 and the bore of the hub 54 from wear. This feature is of particular advantage when the brush holder is mounted on a machine which is subject to heavy vibration.

The brush holder may also be used to check a rebound of the brushes on high speed machines, caused for example, by irregularities in the commutator surface. WVhen used for this purpose the pressure finger 9a is actuated as before described. The auxiliary spring limit screw 42 is then advanced nearly to contact with the brush engaging tip 12 of the auxiliary spring 11. Vith this adjustment any more than a slight backward movement of the brush will be stopped by the end of the auxiliary spring limit screw 42. Further backward movement of the brush will require compression of the snubber spring 40 which can be made as stiff as desired by adjustment of the nut 45.

In Figure 3 is shown a modification of the snubbing device of-Figure 1, wherein the pressure finger is formed of an inner part 56 and an outer part 56a secured to the inner part by means of a bolt 57, the connection between these parts constituting, in effect, a hinge. Nuts 58 partially compressing the comparatively stiff spring 59 serve to hold the two parts 56 and 56a in stiff integral relation until a predetermined reaction brush pressure has been exceeded when the part 56a yields slightly as the spring 59 flexes.

When a block of pure abrasive is used to true the commutator or when the conducting brush employed for truing the commutator has a high abrasive content, it may be desirable to have the abrasive member hurdle the low spot of the commutator so as to practically eliminate all wearing contact between the abrasive and the low spot. For this purpose I provide a means which will prevent a sudden advance of the brush into the low spot of the commutator as the low spot passes under the active face of the brush. Such a means is shownin Figure 1 wherein reference character 48a represents a short tube which surrounds the threaded tube 15 and is attached thereto near its upper end, a short grooved tube 48?) telescoping tube 48a. Between the tube 485 and 48a is a film of asphalt or other sluggishly yielding material which adheres to the outer surface of tube 48a and the inner surface of tube 48?). Clamping the short tube 48?; in the groove is a strap 480, the outer end of which is formed with a downwardly projecting part 48d. The downwardly projecting part 4865 is adapted to engage the side of the pressure finger 9a to prevent rotation of the strap 480 under the influence of the spring 30. It will be then seen that with the strap 48c clamped in the manner showu that the pressure finger 9a which can advance under the influence of spring 30 only by rotation of the tube 15 will advance but slowly because the rotation of the tube 15 is hindered by the sluggishly yielding asphalt. t will be understood that in employing the device in this manner spring 10 will be disconnected and reliance will be had for advancing the pressure finger entirely on the spring 30. When the asphalt hindering effect is not needed the strap 480 is loosened or removed.

It is obvious that, by increasing the pitch of the threads on tube 15, the pressure finger 9a, instead of being held positively against backward movement, will be retarded or hindered in its backward movement.

In the modification shown in Figures 4, 5 and 6, the means for positively advancing or holding the advancement or retarding the backward movement of the pressure finger comprises a cam 60 attached to the pressure finger 9?) by screws 61. A cross head cam follower (32, adapted to slide frictionally on the cam 60, is mounted in the stirrup guide 64 and is vertically adjustable in the guide 64 by means of a screw 63. Guide 64 swings on a pin (35, held by the eyed strap 66 secured to the brush holder frame 10 by the screw 67, which screw also serves to secure the terminal 68 of the brush pig-tail 69. The spiral spring 70 which is secured at one end to the stirrup 64 and at the other end to the brush holder frame normally pulls the stirrup guide 64, tending to rotate it in a counter clock-wise direction and keeps the cross-head cam follower 62 always in close contact with the cam 60. The oro'ss head cam follower 62 is preferably formed with a leather facing 71'for the purpose of increasing the friction between the cam and the follower. ll hen there no leather or other frictional surf-ace forming'the contact between the ,cam ant-the cam follower such contact conif it desired to prevent all re ment of the brush.

sisting of metal sliding on metal, the angle between the legs of the stirrup guide and a normal to the surface of the cam, at the point of contact oft ie cam and the cam follower, should not be'greatcr than about 15 degrees trograde move This condition deter mines the form of the cam. Vfith a friction surface such as'leather, on the cam or onthe cam follower oron both, this angle can be considerably increased. in fact the angle can be nearly as large'as what is known as the angle of repose, that is, the angle whose tangent is the coefiicient of friction; or greater than the an le of repose if 1101130S1t1V8 advancement of pressure-finger de The cam follower ad usting screw 63 is swiveled to the cam follower 62 as by peening over the reduced lower endi73 of the screw, the screw 63 being threaded as shown into the upper end of the stirrup guide 6 1. The purpose of the cam follower adjusting screw 63 is to vary the position of the cam follower 62 in the stirrup guide 64 in order to vary'the position of the cam 60 and therefore the position of the pressure finger 97) to conformto a full length brush or partially worn brush, The snubber relief spring consists of a fiatpiece of spring steel 40?) apertured at 43?) to bodily or slidably receive the snubber tension screw 41?) threaded at its lower end into thepressure finger 9b. The tension of the snubber relief spring 107) is adjustable by nuts 15?).

In using the brush holder in the modification' shown in Figures 1' to 6 the pressure finger 9b is placed under tension by adjustment of the actuating spring arms 49?) or 50b in the usual way, the pull of spring 70,

which is adjustable by placing the upper end of the spring in one or another of the notches 74, is adjusted to cause the cam follower to follow up in close contact-with the cam 60.

If desired, however, the spring 10?) need not be used, dependence being had on the spring to advance the pressure finger, as well as t3 hold all advancement made.

The operation of this form of inventionis easily understood. The brush is advanced by pressure of the finger 9b acting under theinfiuence of the spring 70 or the combined infiuence of spring 70 and spring 10?). Backward movement'of the brush in a direction away from the commutator is prevented or strongly resisted by engagement of the cam on the pressure finger with the follower on the swinging stirrup guide 64.

The brush holder shown in Figures 7 to: 11 includes some means as the clamp '91 and the cap screw 92 of attachment to some stationary part of the machine as the brush-holder stud 93. A brush-holder x94: serves to direct the advancement of the brush 9 1a towards the commutator 95, the thrust of the pressure finger 96 impelling the brush towards the commutator said ressure fin er beingpivotally mounted on the stationary part of the brush holder and actuated by the spring 97, the arm 98 of the spring 97 exerting a thrust against thenotch' 99 of the disc 100 riveted to the pressure finger 96. The

reaction thrust of the other arm 98a of the spring 97 may be exerted either on the-fixed notches 101 or on the notches 101a which fringe the rim of the semi disc 102 integral with the hub 103 with the cams 104: on its end, said cams 104 nesting with the complementary fixed cams 104a. "The hub 103, and consequently the semi disc 102 and the notches 101a, has a slight rotary movement on the 106 extending through a. slot in the head of pivot 105. The hub 107, integral with the pressure finger disc 100, rotates on the same geometric axis as the hub 103, but between the bore of hub 107 and pivot is interposed a bushing 108 with groove109 and an internal shoulder at 110, said shoulder 110 butting against the corresponding shoulder 110a of the pivot 105 when the nut 111 threaded on the reduced end 112 of pivot 105 is tightened. 111a is a lock washer; serves for filling the clearance space or groove 109 between the bushing 108 and the bore of v i desired. 'Thebodies of the screws 115 are preferably squared to fit the width of the slots 116 so that they will not turn when a wrench is applledto the nuts 117.

The adjustment of the screw 119 serves'to limit the movementof'the pressure finger auxiliary spring 120. When the screw 119 is advanced till the end strikes the bottom of the spring bow or hammer 121 in its undefiected position then the auxiliary spring 120 is put completely out of action. Near the end of the pressure" finger 96 are several threaded holes 123, in either of which the screw 12% may be placed. Bythis arrangement the stiffness of the auxiliary spring 120 The hole 113.

pivot 105 held stationary by the cotter pin may be varied in effect. By advancing screw 1241- till the end comes into contact with the spring 120, the spring is practically made stiller. If the screw 1% does not quite touch the spring 120, the spring will move comparatively easily on a backward thrust of the brush till the spring comes into contact with the screw 12 1; thereafter the spring will yield stifiiy till it comes into contact with the end of screw 119. Any further backward motion of the brush beyond this point requires the movement of the pressure finger. By this means varied and progressive degrees of resistance to the rebound of the brush on high speed machines can be secured.

A fibre washer 125 receives the thrust of hub 103 and transmits it to hub 107.

For modifying the viscosity of the asphalt hindering means thermal means, such as the electric lamp 128, may be used. Heat received from the lamp may be varied by its position or by the variable interposition of a screen, such as the shade 129, or by current control, as by the rheostat 130.

V The operation of this brush holder for various purposes will now be described.

Vhen it is desired to have this brush holder function in a manner similar to the type of brush holder in common use, the nut 111 is loosened and the arm 98a of the actuating spring 97 is placed in one of the notches 101. Since the nut 111 is loosened the bushing 108 is free to turn on the pivot 105, as the asphalt or other viscous substance between bushing 108 and the hub 107 of the pressure finger disc causes the bushing'and the hub to turn as a unit. Since the arm 98a now impinges against the fixed notches 101 and not against the notches 101a of the slightly rotatable semi disc 102 integral with the cam hub 103, this hub 103 will exert no axial thrust on the pressure finger hub 107 which is integral with pressure linger disc 100, and so there will be no friction produced on the disc 100 by the bolt heads 11 1.

Suppose now that it is desired to use the brush holder to true up a commutator with flat spots in it and yet have the brush fol low up the fiat spots of the commutator not Jreaking contact with the commutator at the flat spots as would be the case if the flat spots were hurdled. In this case the screw 119 is advanced till the end comes into contact with the bottom of the bow hammer 121 of the auxiliary spring 120, thus annulling the action of the auxiliary spring. The arm 98aof the actuating spring is then placed in one of the notches 101a. This slightly rotates the hub 103, the cams 104 on its end coming into contact with the fixed cams 104a, the fixed cams 104a then giving an axial thrust to the hub 103, which impinges on the hub 107 via washer 125. hub 107 in turn causing the pressure finger disc 100 to rub against the bolt heads 114, thus causing enough friction to substantially hinder the movement of the pressure finger 96. The friction prevents the full force of the actuating spring 97 being delivered to the end of the pressure finger that makes contact with the brush. Consequently, when the brush is moving forwards, as is the case when it is moving into a flat spot of the commutator, there will be a comparatively small pressure exerted by the brush on the commutator, and, consequently comparatively small wear by the brush on the flat spots of the commutator. But when the pressure finger 96 is moving baclnvards conditions are reversed, friction in this case aiding the spring 97 to resist the backward motion of the pressure finger. Now when the brush is moving backwards is the time when the high spot of the commutator is coming under the brush. Consequently there will be a comparatively large pressure between the brush and the h spot of the commutator, l consequen. a comparatively large wear by the brush on the high spot of the commutator. Naturally, with comparatively little wear on the low spot of the c-rnnmutator and comparatively much wear on the high spot of the commutator, there is tendency for the commutator to become true. If the brushe are suliiciently abrasive the commutator will become true.

If it is desired that the brush wear only on the high spot of the commutator, thus hurdling the low spot, the nut 111 is tightened,

clamping the bushing 108 to the pivot 105.

its the clearance space between the bushing 108 and the bore of the hub 107 is filled with asphalt or some other viscous substance, it is clear that the hub 107, as well as the disc 1.00 and the pressure finger 06 integral with it, cannot move except as the asphalt yields. N ow the asphalt yields so slowly compared with the speed of the electric .iachine that the pressure finger is not able to advance the brush into contact with he commutator when the low spot of the commutator comes under the brush. Consequently there will be no wear by the brush on the low spot of the commu at r, all the wear by he brush coming on the high spot of the commutator. As a result the commutator will finally become true. The arm 98a is assumed to be in notches 101a in the above described operation.

By removing the arm 98!: from notches 101/z to notches 101, the fricti n of the screw .ds 114 on the pressure finger disc w 3e eliminated, the asphalt alone then a as the hindering means to hinder the me .--.on of the pressure finger 96. However, the use of asphalt alone as the hindering agent is less advantageous sometimes tl n the use of both asphalt and friction as th eri Suppose now there ens .e vibration in the machine and in ii sh holder mounted thereon, and conseqiuntly the possibility of considerable wear on the pressure nger hub and. the pivot on which it rotates. tis desi ed that the continual movement of the pressure finger relative to the stationary part of the brush holder be eliminated so. as to avoid the wear between: the hub and pivot. In this case the spring arm 98a is placed on the notches 101a, thusthrowing into action the friction hindering means; the viscous substances hindering means optionally may or may not be used by tightening or loosening the nut 111. The screw 119 is backed offso as to give freeinovement to the auxiliary spring120 Under these conditions .here will be little'movement between the pivot and the hub of the pre-ssure'finger, and consequently very little wear, most of the vibration being made by the auxiliary spring 120 instead of by the pressure finger. By disposition of screw 124 in one of the holes 123 and adjustment of screw 124 the rebound of the brush can be'regulated.

Suppose now the brush holderis mounted on a high-speed machine with slight irregularities in the commutator that causes a strong reboundof the brushes. In this case the spring arm 98a is placed in notch 101a, thus throwing the friction hindering means into action. Then, the brush being in position in the brush holder, the screw 119 is advanced till the end nearly touches the'bottom of the bow hammer 1210f the auxiliary spring 120. It will be'seen that a slight re bound of the brushcan take place before the bow 121 of the auxiliary spring comes into contact with the end of the screw 119. From this point on the further rebound of the brush is strongly resisted by the spring 97' and the friction'hindering m ans as well. The viscous substances hindering means may optionally be used or not used by tightening or loosening the nut 111. c

Mention has been made of the fact'that the friction bolts 115 are radially adjustable inthe radial slots 116. The distance apart of the bolts 115 determines the ratio between the friction torque and the torque produced by the actuating spring 97. This ratio becomes greater as the distance between the screws 11-5 becomes reater. The should in no case be placed so far apart that the friction becomes large enough to prevent the pressure finger from moving forward at all.

The active faces of the cams 104 and 104a should preferably be short sections of square screw threads. j r

In the modification shown in Figures 12 and 13 another method is used for frictionally hindering the motion of the pressure finger 131. Secured by the screw 132 to the topof the pressure finger 131 is the U-shaped clamping box 133. he inner width of this clamping box is a little greater than the width of the pressure finger 131. In the bottom of this U-shaped box and near the side 134 is a slot 135 of a size to slidingly receive the segmental friction strip 136. 'Slidably. mountedby means of the screws 137 and the slots 138 above the pressure finger 131 is the gripping is a thin strip of flexible metal 145, such as spring steel or phosphor bronze. This metal strip 18 flex1ble enough to freely transmit the lateral thrust of the curved end 140 ofthe gripping bar to the segmental friction strip 136. The segmental friction strip 136 is attached by'the screw 146 to the brush holder shank 147. The thrust of the actuating.

spring 148 is transmitted by the spring arm 149 to the end of the gripping bar 139 at the notch 150. It is evident that the axial thrust received bythe gripping bar at the end 150 will be dividedat the other end into an axial thrust and a lateral thrust. The relativeproportion of these two thrusts will depend on the position of the thumb-screw 142. If

the thumb-screw 142 is far advanced, the axial thrust willpredominate over the lateral thrust; if the thumb-screw is little advanced, the-lateral thrust. will predominate over the axial thrust. At some intermediate position of the thumb-screw 142 the friction on the segmental friction strip 136 will not be quite large enough to stop the movement of the pressure finger 131. Thisposition of the thumb-screw 142 will generally befthe best posit-ion for truing up a commutator. The

reason for the use of the flexible metal strip 145 is to avoid the possibility of a variable friction, due to the possible looseness of mountingof the gripping bar 139.

In the modification shown in Figure 14 the friction hindering means is applied in the form of a flexible element 161, such as a stranded wire cord or thin metal ribbon wrapped around or partly around the brush holder stud 162. The attachment is made to a brush holder of a type in commonuse without any mutilation of the brush holder,

by using the screw that holds the brush pigv tail to secure the attachment to the brush holder shank. v

A, vertical rod 163 is riveted to the footer plate 164, which is secured by the screw 165 to the brush-holder shank 166. To the pressure finger 167 is secured one end of a stranded steel wire or thin'phosphor bronze metal ribbon 161, said flexible wire extending under and half around the brush-holder stud 162 to thespring 169, to which this end of the wire is secured. The other end of; the

spring 169 is secured by the screw 170 to the collar 171 slidably mounted on the rod 163 and adjustable thereon by means of the screw 172. When used to true up the commutator 173 an abrasive brush or abrasive block 174 is preferably substituted for the usual brush. The pressure finger actuating spring 175 may or may not be used when a commutator is being trued up. If the pressure finger actuating spring 175 is not used, the abrasive brush or abrasive block being advanced by the use of the spring 169 only and the coefficient of friction assumed to be 20%, then, with the wire cord covering 180 degrees of circumference, pressure exerted by a high spot of the commutator to force the brush backwards will be about 3 times the pressure exerted by the flat spot of the commutator to stop the advancement of the brush towards the commutator. This ratio is sufficiently large to true up a commutator. If the stranded wire covers three-quarters of the circumference of the brush-holder stud 162, this ratio will rise to 6 A similar arrangement may of course be used on the other side of the brush-holder shank.

The modification shown in Figures 15 and 16 uses the same principle used in the modification of Figure 14. In the modification shown in Figures 15 and 16 the central portion of the shank 181 is widened into a grooved hub 182 in which is disposed the turn or bight of the stranded wire 183. To protect the wire 183 from a flash-over a shield 184 surrounds a considerable portion of the wire. This shield is attached by the screws 185 and 186 to the brush-holder shank 181.

In the modification shown in Figure 17 one end of a stranded wire cord 191 is attached by the screw 192 to one end of an offset bracket 193 secured by the screw 194 to the brush-holder pressure finger 195. The said stranded wire cord then runs under the rounded end of the brush-holder shank 196 and over the cylindrical stub 197 projecting from the side of the brush-holder shank 196, the end 198 being attached to hook 199 in the end of the spiral spring 200, said spring being tensionally adjustable by looping the eye in the other end of said spring over the notches 202 in the edge of the brush-holder shank 196. The washer 203 secured by the screw 204 serves to keep the stranded wire 191 in position.

The amount of friction. exerted by the stranded wire 191 can be easily figured out by assuming certain conditions. The said wire 191 covers 180 of circumference on the brush-holder shank and 90 of circumference on the cylindrical stub, or a total of 270 of circumference. With a coeflicient of friction of 25%, it will take, say, three pounds at one end of the wire 191 to overcome one pound at the other end. A pull of 6 pounds flat spot of the commutator to stop the ad- I Vance of the brush will be substantially in the ratio of 18 to 2, or 9. This ratio is on the assumption that the pressure finger spring 205 is not in action. If this spring 205 should be in action and exert a pressure of,

say 1 pound near the wire 191, this ratio will be reduced to 19 to 3, or about 6. By giving a turn of the wire 191 around the cylindrical stub 197, 360 of circumferential contact are added to the previous 270; to overcome a pull of 6 pounds exerted by the spring 200 would require a pull of 90 pounds at the other end of the wire 191 under these conditions. It is evident that no hindrance whatever is made by the wire 191 to the forward motion of the pressure finger. The wire 191 runs in a groove 206 extending down the rear side of the brush-holder shank and under it. This groove is kept covered by the metal strip 207. One of the purposes of the metal strip 207 is to prevent that portion of the wire adjacent to the rear side of the brushholder shank from taking a bow form when unwound from the rounded portion of the brush-holder shank 196.

If the strands of the wire cord 191 are not very fine the wire may take a permanent set because of being bent around the rounded portion of the bruslrholder shank. This permanent flexure results in what is the equivalent of lost motion. Such lost motion effect due to the permanent set of the wire taking a bow form can be avoided by having prooved guides tangential to the cylindrical portions of its path. This is shown diagrammatically in Figure 18 in which the grooved or tubular guides 208 prevent the tangential portions 209 of the wire taking a bow form when unwound from the cylinder 210. With the proper reverse crooks in these tubes as indicated at 211, the effect of the bow not only may be avoided, but the bow itself removed.

It is evident that a thin metal ribbon or fibre cord might be used in place of the stranded wire cord 191. Or a small light metal chain might be used instead of the stranded wire. lVith the chain or fibre cord there would be no how effect to be taken care of. The objection to the fibre is on account of a. slight yielding inherent in such material.

In the modification shown in Figures 19 and 20 the brush-holder shank 221 is in trough or channel form. Vithin this hollow shank is mounted the spring 222 housed in 240a are used as the hindering means.

the cylindrical shell'223, the hub 22l-o'f which makes a bearing fit on the shaft 225. One end 225a of the enclosed spring 222 is hooked into the end wall of the cylindrical shell 228, and the springs other end 226, diametrically bent, is inserted in the slot 227 in the end of the shaf 225. The spring 222 put under stress by inserting the arm secured in slot 22'? to the shaft 225, in the notches228a that fringe the rim of the sheet 'jmetal disc 229 riveted to the side of the brush-holder shank 221.

finger 233. Straightening pins 23 serve to "straighten the wire 230 or prevent a bow in the portion between the said straighten ng pins and the hook 282. On a backward motion of the brush a bow in this portion of the wire would first havo'to' be stra htened before the backwardmotion the brush could be effectively checked, how were not removed by straightening pins ormade' ineffective by said pins or by a tube or groove.

Still another principle may beutilizedin a hindering means. Certain metals or alloys, such as lead or solder, have the property, when subjected to a force less than that necessary to immediately bend or distort them of bending or yielding, butonl slewly.

This principle may be used in hindering the motion of. the pressure finger of the brush holder or abrasive by fastening wire soloer to the pressure finger or ab asive, the body of the wire being drawn by the pull the pressure finger or abrasive in a wave form to the left and right of alternate pins or rolL ers arranged in a row. 7

In the modlfication shown in Figures and 22 two pieces of wire solder 240 two solder wires have their ends 241 241a bent at right angles and ins rted in holes in the outer end of the abrasive 2/12 The wire solder 240 then passes alternately to the left and right of a plurality. of grooved rollers 24o; and the wire solder24l0a alternately to the rightand left of a pli l ity of grooved rollers 243m The pins 2% and 244a on which these rollers turn are attached to the stemmed Usshaped supporting mem her 245, this member straddling the front wall 246 of the brush-holder be to which it is fastened by the thumb-screw 24?. The perspective view in Figure 22 shows the assemblage of the abrasive 242, the wiresolder However, the wires bend, though slowly, the

rollers slowly revolve and the abrasive makes corresponding advancement to contact with the commutator at the high spots of the commutator. The speed of advancement of the abrasive towards the commutator may be varied by changing the number of rollers 1 around which the wire solder is wrapped, the fewer the number of rollers thefaster the solder wire advances; If the stress on the actuating spring of the pressure finger is increased or decreased the abrasive advances faster or slower.

It is evident that if the pins 244 and 244a around which the rollers revolve were covered with asphalt the motion of the rollers would be retarded and the speed of advancement of the abrasive consequently decreased. It is evident that if, instead of a solder wire, a llexible wire or-cord had one end made fast to oneof. the rollers and a turn or two of the wire taken around the roller, the other end being secured to the abrasive, the abrasive will be hindered in its advancement towards the commutator. The pin around which the roller revolves is preferably made'rotatably or translatably adjustable. for the purpose of taking'up any possible slack in the wire or cord when initial adjustment is being made Instead of the solder wires being attached to the'abrasive as'shown inFigures 21 and 22 they may be attached to a wedge shaped pushed member 250 in Figure 23, said pusher member being designed to receive the thrust of the pressure finger and transmit the thrust to the abrasive. In this case delay hindering means cooperates with friction hindering means. 'InFigure 24the solder wires are not connected to the pusher 255 but pass by it or through it to connection with the abrasive 256. The wedges shown in Figures 23 and 24 and wedges of a similar character are made thesubject matter of a separate application Serial Number 278,751- of even filing date herewith.

In the modification shown in Figure 25 the pusher member 259 is square, thus avoiding friction hindering means. The hinder ing effect is secured by a bit of asphalt 260 placed between the side of the pusher memher 259, and the inside limb 261 of the U- shaped protective member 262, the two limbs of which straddle the front face of the brushholder box 263, being secured thereto by the.

thumb-screw 264 threaded into the outer limb 

